Multi-focus X-ray tubes generally comprise a single anode in linear or arcuate geometry which can be irradiated along its length by two or more switched electron sources. In a typically configuration, hundreds of electron sources or guns might be used to irradiate a single anode with a length of over 1 m. Often the electron guns will be actuated individually and sequentially in order to create a rapidly moving X-ray beam. Alternatively, the electron sources can be actuated in groups to provide X-rays beams with varying spatial frequency composition.
Known multi-focus X-ray sources tend to use combination metal and ceramic housings fabricated using standard vacuum seals such as con-flat assemblies or metal gasket seals. Such assemblies are extremely expensive to put together since they require precision machining to meet stringent vacuum requirements.